the preheat coil
control valve will start opening when the reheat coil cannot maintain the preset hot deck temperatures.
If the outdoor air is so cold that that the mixture of outdoor air and bypassed air containing the minimum outdoor air flow rate is colder than the SAT setpoint, then the preheat coil
is initiated to heat the outdoor air until the mixed air reaches the SAT setpoint.
Features include dual boilers, a preheat coil
, a fully saturated brew group, and software that distributes power to the elements that need it most.
Sieve [*] Conventional System with First-cost comparison System Exclu-Sieve [*] Equipment cost $56,000 $110,000 [*] Installation/ductwork $28,000 $23,000 Required chiller/cooling tower $91,000 $43,000 capacity (260 tons) (123 tons) Electric preheat coil
[**] $7,000 (543 kW) $0 (0 kW) Total first cost $182,000 $176,000 First cost savings with $6,000 Exclu-Sieve [*]
We occasionally have temperatures below freezing, and many of our AHUs are equipped with a hot water preheat coil
located after the mixed air plenum and in front of the cooling coil (see Figure 1).
The baseline data center ventilation unit would have a preheat coil
to protect the AHU from freezing and still be able to operate year-round.
Using a single coil had the added benefit of eliminating the fan energy penalty associated with the more typical practice of using a heat recovery heat coil supplemented with a preheat coil
min] = minimum temperature leaving preheat coil
, [degrees]F ([degrees]C)
That DOAS unit is sometimes outfitted with a preheat coil
and an unnecessarily high discharge air setpoint in the winter (e.
In Region IV, the OA DBT is below freezing much of the time, so to avoid low-temperature incidences (freezing) at the cooling coil (if chilled water), a freeze-proof preheat coil
is required to elevate the OA DBT to about 40[degrees]F (4.
Although this approach requires the installation of a small preheat coil
, it allows the wheel to continue operating at full energy-recovery capacity even during the coldest times of the year.
The preheat coil
is set to 10[degrees]F below the supply air setpoint temperature.